Many residences include on the outside doors a dead bolt lock as an additional safeguard against illegal entry by burglars. These locks are nothing more than a large bolt which is square on its end and which can be moved horizontally into a receiving hole in the door fame by means of manual lever on the inside of the door or by a key on the outside of the door. The bolt cannot be moved by inserting a thin plate or card between the door and the door frame to cause the bolt to recede to its unlocked position as can be done with the usual door latch having a angular face to the latch. The dead bolt lock must be moved by means of a key or a lock pick if the door is reasonably fitted to the frame. Lock picks of various types are commonly used by burglars, and those with experience can rapidly open dead bolt locks with such devices. Furthermore, with the proliferation of the keys one can expect many burglars to have keys for many dead bolt locks.
It is an object of this invention to provide an accessory to be used in connection with dead bolt locks that will cause considerable delay in opening such locks even though a proper key is used. Any delay would discourage a burglar because it increases the chance of being discovered in attempting an illegal entry.
The novel features believed to be characteristic of this invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization, and method of operation, together with further objects and advantages thereof may thus be understood by reference to the attached drawings and to the following description.